Hydrogen production by radio frequency plasma stimulation in methane hydrate at atmospheric pressure

Significance Statement

The attached conceptual drawing summarizes our proposal for a methane-hydrate plant. With this method, the methane-hydrate is broken down and collected as hydrogen gas, with the carbon content being solidified in the ocean floor. With this method there is no concern about emitting greenhouse gases. Electrical power is needed for generating the plasma. This electrical power can be generated using solar, wind or ocean current as renewable energy sources. Since the hydrogen gas is collected, there is no concern about gases such as methane hydrate re-hydrating as it is raised. This eliminates the need for temperature and pressure control of the pipe line and separation equipment once it has been collected. There is also no need for a hard pipeline as the hydrogen gas will rise in a stable state without chemical reaction occurring. Since hydrate does not flow by itself, there is a limit to how much gas can be collected at one location. Previous types of plants using the pressure reduction method or the heating method, including the pipe line, are difficult to move. With the in-liquid plasma method, the hydrate is melted and broken down by the plasma, so the plant can be moved simply by moving the plasma electrode. Furthermore, the amount of energy input can be dramatically reduced if geothermal energy is used to assist in the melting of the hydrate. The key is determining which renewable energy to incorporate into this system.

Methane hydrate, formed by injecting methane into 100 g of shaved ice at a pressure of 7 MPa and reactor temperature of 0 °C, was decomposed by applying 27.12 MHz radio frequency plasma in order to produce hydrogen. The process involved the stimulation of plasma in the methane hydrate with a variable input power at atmospheric pressure. It was observed that production of CH4 is optimal at a slow rate of CH4 release from the methane hydrate, as analyzed by in light of the steam methane reforming (SMR) and the methane cracking reaction (MCR) processes in accordance with the content of gas production. In comparison with the steam methane reforming (SMR), it was found that methane-cracking reaction (MCR) was dominant in conversion of CH4 into hydrogen. An H2 content of 55% in gas production was obtained from conversion of 40% of CH4 at an input power of 150 W. The results clearly show that hydrogen can be directly produced from methane hydrate by the in-liquid plasma method.